In a conventional magnetic storage system, a thin film magnetic head includes an inductive read/write transducer mounted on a slider. The thin film head is coupled to a rotary actuator magnet and a voice coil assembly by a suspension and an actuator arm positioned over a surface of a spinning magnetic disk. In operation, a lift force is generated by the aerodynamic interaction between the magnetic head and the spinning magnetic disk. An exemplary thin film magnetic head includes a plurality of write poles, also known as P1 and P2, that encapsulate a magnetically inductive coil disposed by a recess from the air bearing surface (ABS). During a write operation, the inductive coil cooperates with the poles P1 and P2 to generate a magnetic field that directs the magnetic flux from the pole P1 to the pole P2 through the magnetic disk onto which digital data are to be recorded.
In a conventional magnetic media application, the magnetic recording disk is comprised of several concentric tracks onto which magnetization bits are deposited for data recording. Each of these tracks is further divided into sectors wherein the digital data are registered. As the demand for large capacity magnetic storage continues to grow at an ever increasing pace, the current trend in the magnetic storage technology has been proceeding toward a high track density design of magnetic storage media. In order to maintain the industry standard interface, magnetic storage devices increasingly rely on reducing track width as a means to increase the areal density without significantly altering the geometry of the storage media.
As the track width becomes smaller, the size of the thin film head must also be reduced accordingly. This reduction necessitates an accompanied decrease in the physical dimension allowance of the inductive coil, also known as the yoke length. While the coil yoke length decreases, the demand for high areal density continues to impose the same or greater requirement for the coil density, which is the number of coil turns per coil area.
To address the coil size and density requirements, various attempts have been developed. One such attempt is exemplified by U.S. Pat. No. 4,416,056 to Takahashi, which discloses a conventional inductive coil comprising of two plane coil layers that are formed by a plurality of spirally wound conductors arranged in an alternating pattern. By doubling the number of coil layers, the coil density increases proportionally.
In general, the conventional inductive coil according to the Takahashi patent is manufactured using a chemical wet etching process to create the pattern of the coil winding. Prior to the wet etch, the coil pattern is formed by a photolithographic process involving the deposition of a photo resist layer onto a conductor substrate surface. By exposing the photo resist layer to an ultraviolet light source through a photo mask, the coil pattern photographic image is formed. The wet etch is then applied to the exposed photo resist to remove the exposed photo resist material, leaving behind on the substrate the patterned conductors that form the coil winding.
The inductive coil process according to the Takahashi patent presents a number of disadvantages that significantly offset the benefit of high areal density of the conventional coil design. Some of these disadvantages are described as follows:
During the preparation process prior to the photolithography, a layer of dielectric material is deposited onto the conductor substrate surface to provide insulation between the coil layers prior to the deposition of the photo resist layer. With reference to FIG. 1, which illustrates a conventional coil process, due to the physical imperfection of the dielectric material, there likely exist various tiny openings or pinholes 1, formed in the dielectric layer 3. Thus, during the wet etch process which is designed to remove the exposed photo resist material, the etching solution may seep through the pin holes 1 in the dielectric layer 3 to permeate into the underlying conductor surface 5, thereby likely resulting in a damage to the coil. In some instances, the etching solution may penetrate far enough to cause damage to the write pole P1. As a consequence, a considerable endeavor is required to ensure that the dielectric layer is free of pinholes 1, which in itself is a difficult task to accomplish.
Yet another disadvantage with the Takahashi design is the coil size limitation due to the alignment process and the physical limitation of the photo resist. The coil windings are separated by a gap of width “d.” This gap is formed after a wet etch during which the exposed photo resist material is removed therefrom. In order to form this gap, a photo mask 7 must be aligned with the photo resist layer with high precision. As the demand for high coil density increases, the coil size becomes smaller and so does the gap width “d.” As a result, the alignment becomes more challenging, resulting in a potential misalignment which could adversely affect the quality and production of the conventional inductive coils.
Furthermore, the photo resist typically reaches a physical limitation of about 0.2 μm. Thus, both the alignment problem and the photo resist limitation impose a size constraint on the conventional inductive coil. As a result, conventional inductive coils as exemplified by the Takahashi patent, may not be further enhanced beyond their maximum limit as dictated by the foregoing size constraint, thus preventing these coils from meeting the demand for greater areal density in high capacity disk drives. Currently, a conventional coil design may have reached its size limitation of 17 μm with a coil density of 9 turns per coil.
As the demand for high capacity magnetic storage continues to grow, the size of inductive coils needs to be reduced in order to increase the areal density, while the coil density remains the same or greater. Consequently, a demand for an improved inductive coil design and process is needed. This improved coil design preferably utilizes an enhanced process that would promote high magnetic efficiency for high areal density recording without potentially causing damage to the coil conductors. Moreover, the improved coil design should be able to meet the demand for a decreased coil size imposed by the technology advancement without being affected by the size constraints currently faced by conventional inductive coil design.